smb: client: use kvzalloc() for megabyte buffer in simple fallocate

smb: client: use kvzalloc() for megabyte buffer in simple fallocate

Currently in smb3_simple_fallocate_range(), a 1 MB buffer is allocated
using kzalloc(). Under heavy memory fragmentation, a contiguous 1 MB block
of physical memory (an order-8 allocation) may not be available,
causing the allocation to fail.

This failure was observed during xfstests generic/013 on a 4GB RAM
test machine running fsstress:

fsstress: page allocation failure: order:8,
mode:0x40dc0(GFP_KERNEL|__GFP_ZERO|__GFP_COMP),
nodemask=(null),cpuset=/,mems_allowed=0

Call Trace:
 <TASK>
 dump_stack_lvl+0x5d/0x80
 warn_alloc+0x163/0x190
 __alloc_pages_slowpath.constprop.0+0x71b/0x12f0
 __alloc_frozen_pages_noprof+0x2f6/0x340
 alloc_pages_mpol+0xb6/0x170
 ___kmalloc_large_node+0xb3/0xd0
 __kmalloc_large_noprof+0x1e/0xc0
 smb3_simple_falloc.isra.0+0x62b/0x960
 cifs_fallocate+0xed/0x180
 vfs_fallocate+0x165/0x3c0
 __x64_sys_fallocate+0x48/0xa0
 do_syscall_64+0xe1/0x640
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
 </TASK>

Node 0 Normal: 3375*4kB ... 7*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB

Since this scratch buffer does not require physically contiguous memory,
switch the allocation to kvzalloc(). This retains the performance
benefits of kmalloc() under normal conditions, while gracefully falling
back to virtually contiguous memory when physical allocation fails.

Fixes: 966a3cb7c7db ("cifs: improve fallocate emulation")
Cc: stable@vger.kernel.org
Signed-off-by: Fredric Cover <fredric.cover.lkernel@gmail.com>
Tested-by: Fredric Cover <fredric.cover.lkernel@gmail.com>
Signed-off-by: Steve French <stfrench@microsoft.com>